In recent years, VLSIs have been rapidly made higher in packaging density and more highly integrated, and there is a demand for more multi-layered aluminum wiring and for decreasing minimum working line width as its wiring patterns are made finer. Accordingly, multi-layer wiring interlayer insulation films used in such LSIs are required to be formed by a smoothing technique which fills wiring gaps without vacancies and also makes their surfaces smooth.
As interlayer insulation films that are required to be made smooth, films (SOG films) formed by what is called the spin-on-glass method (SOG method) are conventionally employed in which a coating solution obtained by hydrolyzing an alkoxysilane and an alkylalkoxysilane in an organic solvent such as alcohol in the presence of water and a catalyst is applied by spin coating, followed by heating to cause coatings to cure. In particular, organic SOG films are mainly used in which the side chain of an organic component (an alkyl group such as methyl) is bonded to the backbone chain of a siloxane bond, i.e., an organic component (an alkyl group such as methyl) is left in the film, which can prevent cracks from occurring and improve smoothing properties to enable thick-layer formation.
The SOG films have advantages such that they cause less volume shrinkage, show a hydrophobicity and have a low dielectric constant. However, when dry etching is carried out using oxygen plasma during the course of the fabrication of an LSI in order to strip a photosensitive resist used to form contact holes that connect aluminum wiring provided at the lower layer and upper layer of the insulation film, this oxygen plasma causes alkyl groups in the film to be released, thus causing cracks. Accordingly, the insulation film is basically formed not in a single layer structure but in a three-layer structure so that the organic SOG film is not laid bare to the surface at the time of oxygen plasma processing, i.e., (i) an SiO.sub.2 film serving as a base for SOG film coating is formed by plasma-assisted CVD, (ii) the organic SOG film is formed thereon by coating and etchback-treated and (iii)another SiO.sub.2 film serving as an upper coat is formed by plasma-assisted CVD.
FIG. 1 illustrates an example of a process for producing a semiconductor device by the use of such an organic SOG film.
In FIG. 1, reference numeral 11 denotes a semiconductor chip substrate on which circuit electronic components such as a transistor, a diode, a resistor and a capacitor that constitute an electronic circuit are formed; 12, a first aluminum wiring formed on the semiconductor chip substrate; 13, the SiO.sub.2 film serving as a base for coating the organic SOG film, formed by plasma-assisted CVD; and 14, the organic SOG film [FIG. 1 (a)]. Etchback treatment is carried out to subject the whole surface of the organic SOG film 14 to oxygen plasma processing to make the plasma CVD SiO.sub.2 film laid bare at the part corresponding to the aluminum wiring 12 [FIG. 1 (b)]. Over the entire surface having been subjected to etchback treatment, another SiO.sub.2 film 15 serving as an upper coat is formed by plasma-assisted CVD, and a stated etching resist 16 is formed thereon [FIG. 1 (c)]. The plasma CVD SiO.sub.2 film at the part corresponding to the aluminum wiring 12, not covered with the etching resist 16, is removed by etching to make the aluminum wiring 12 exposed, and the etching resist is removed [FIG. 1 (d)]. Then, a second aluminum wiring 17 connected with the first aluminum wiring 12 is formed [FIG. 1 (e)]. Thus a semiconductor device is produced.
However, as the VLSIs are made higher in packaging density and more highly integrated, the space between aluminum wirings becomes so fine that the formation of the plasma CVD SiO.sub.2 film serving as a base for SOG coating makes the fine space between aluminum wirings still finer in the conventional three-layer structure, and hence an SOG coating solution can be caused to flow into the aluminum wiring space only with difficulty, resulting in a defective state of burying the organic SOG film. For this reason, with a decrease in minimum working line width, which decreases as the aluminum wiring becomes finer, it has become difficult to form the interlayer insulation film in the conventional three-layer structure. Accordingly, it is desirable to provide an SOG film having a good oxygen plasma resistance and enabling formation of the interlayer insulation film even in a single-layer structure.
In order to shorten the semiconductor device fabrication process, aiming at a cost reduction, there is a demand for non-etchback type SOG films that necessitate no etchback treatment. Accordingly, taking as a basis an inorganic SOG film (a film basically containing no organic component) having a good ashing resistance, it has been studied to add fine SiO.sub.2 particles, to use B-O and Mg-O bonds in combination or to introduce an Si-N skeleton, but no positive results have been forthcoming.